A number of proposals have been made heretofore for the harnessing of the sun's power, and for example it has been proposed to utilise banks of reflectors which heat water contained in tubes to evaporate the water into steam, transport the steam to the location of an engine, and drive the engine with the steam. Such proposals have not reached the stage of general acceptance, one of the reasons being the long steam lines which are required, and another being the high capital cost. Long steam lines essentially have associated with them a loss of efficiency, and furthermore to boil water it is necessary to create temperatures within the pipe of the order of 120.degree. C. Such temperatures are readily obtainable from the sun's rays, but it is necessary to always direct a mirror towards the sun to achieve the high temperatures. The result of these two disabilities is a very high capital cost and high maintenance costs for operating an installation.
The main object of this invention is to provide means whereby "low grade" heat energy may be translated into useful mechanical energy without the need for attempting to obtain high temperatures, and further to achieve the mechanical energy without the use of long steam lines (with consequential heat losses). It is a further object to provide a power unit which does not involve excessive capital expenditure, and although this invention results in a slightly higher efficiency than has been obtained heretofore, this invention will be seen to be so simple that it is probably less expensive to utilise larger units than to incorporate efficiency improvement into the equipment, but of course both expedients may be used when high power outlet is required.